Global emissions of toxic metal residues to a wide spectrum of aquatic ecosystems have increased dramatically over the past 100 years due primarily to anthropogenic releases associated with mining, metal refining operations and industrial activity. Closely associated with these increases in the release of metal residues into the environment is the widespread increase in the concentrations of metals in fish, wildlife and human populations. Associated with this increase in exposure to metal residues is a wide variety of toxic responses ranging from reproductive problems to impaired mental development. In addition to aqueous exposure, movement of metal contamination up food chains can lead to contamination of wildlife and humans not directly exposed to metal pollution. The increasing industrialization on a global scale will be accompanied by an escalating demand for metals and a subsequent rise in metal waste discharges into aquatic systems. Monitoring of toxic metal species, potentially impacting wildlife and humans, and remediation of metal contamination will be critical activities for the foreseeable future.
Laboratories conducting analytical and toxicological research concerning the presence and toxicity of metal species must have sampling and analytical methods capable of defining the presence and amounts of bioavailable metal residues. In general, current sampling methods are not integrative over sufficient time intervals to sequester adequate amounts to detect trace to ultra-trace levels of metal residues (many of which may have toxicological significance) and to cost effectively detect episodic releases. Also, current sequestration methods are not adequate for integratively isolating sufficient amounts of the mixtures of toxic metals present in aquatic systems for use with bioassay procedures or for toxicity testing.
Considering the prior art in more detail, although there has been considerable effort directed towards development of methods for removing heavy metals from highly contaminated industrial and mining waste streams, relatively little has been accomplished in the development of a complementary monitoring device for trace level metals. The sequestration approaches which have been previously developed for the cleanup of metal waste streams are generally ineffective for the low (part per billion to part per trillion) concentrations present in natural waters. In addition, all of these approaches are impractical for application with long-term, unattended monitoring of metal residues in remote aquatic systems. Integrative sampling for low concentrations of metals has yet to be rigorously demonstrated.
Patents of interest in this general field include the following U.S. Pat. No. 4,303,702 (Courduvelis et al); U.S. Pat. No. 4,500,494 (Scher); U.S. Pat. No. 4,702,838 (Babcock et al); U.S. Pat. No. 5,037,555 (Pasternak et al); U.S. Pat. No. 5,087,372 (Toyomoto et al); U.S. Pat. No. 5,190,660 (Lindoy et al); U.S. Pat. No. 5,316,683 (Haesebroek; et al); U.S. Pat. No. 5,616,533 (Tavlarides et al); U.S. Pat. No. 5,618,433 (Tarbet et al); U.S. Pat. No. 5,668,079 (Tavlarides et al); U.S. Pat. No. 5,738,791 (Schomaker et al); U.S. Pat. No. 5,814,226 (Tavlarides et al); U.S. Pat. No. 5,817,289 (Tavlarides et al); and U.S. Pat. No. 5,834,633 (Davison). Briefly considering some of these references the Davison patent discloses a probe device for use in measuring quantities of a component in a liquid environment, which comprises (1) a membrane which is permeable to the component and (2) a layer of a material capable of binding the component and arranged to receive material which has permeated through the membrane from a face thereof juxtaposed to the fluid environment. The membrane is a polyacrylamide gel, and the material for binding the component may be a particulate material and may be incorporated in the membrane or provided as a separate layer juxtaposed thereto. The material comprises an immobilized complexing agent. This device can be used for determining quantities of trace metals in an aqueous environment. The Schomaker et al patent discloses a method for extracting metal ions from an aqueous solution comprising contacting the aqueous solution with particles of a hydrophobic, isotropic, microporous polymer in which there is immobilized an organic complexing agent selected from the group consisting of organic carboxylic acids, organic phosphorus compounds, oxime compounds and mixture thereof. The Lindoy et al patent teaches a method of removing preselected metal ions from solution by complexing them with an immobilized polyethylnimine. The Babcock et al patent discloses a method for the selective removal of metal ions (e.g., copper) from a plating solution (e.g., a nickel plating solution) comprising contacting the plating solution with liquid organic complexing agents such as oximes or phosphoric acid esters or using a microporous material impregnated with such substances and in the form of gels, sheets and beads. The gel is coated onto a solid microporous support, and the support itself contains the complexing agent. The Scher patent provides a process for the purification of an aqueous solution containing metal ion impurities. The process comprises contacting the solution with a plurality of polyurea and urea-formaldehyde microcapsules which enclose a chelating agent selected from .beta.-diketones, 8-hydroxyquinolines and their thiol analogs, and oximes. The remaining patents further illustrate the state of the art.